Fastener assembly for attaching a non-metal component to a metal component

ABSTRACT

A fastener assembly for attaching components of dissimilar materials includes a fastener having a base portion and a protruding portion, and a mechanism for tightening the assembly. The base portion is shaped to be complementary for mating with an attachment feature formed within the non-metal component such that the base portion is retained within the non-metal component. The protruding portion including a base end and a distal end with the distal end including a threaded portion. The fastener assembly allows attachment of components fabricated from dissimilar materials without forming through holes in one of the components. Additionally, the fastener assembly compensates for differences in thermal expansion rates between the non-metal component and the metal component while providing a tight attachment therebetween.

The invention was made under a U.S. Government contract and theGovernment has rights herein.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to gas turbine engine fasteners and, moreparticularly, to gas turbine engine fasteners for attaching componentsfabricated from dissimilar materials.

2. Background Art

A typical gas turbine engine operates in an extremely harsh environmentcharacterized by very high temperatures and vibrations. A conventionalgas turbine engine includes a compressor for compressing entering air, acombustor for mixing and burning the compressed gases that emerge fromthe compressor with fuel, a turbine for expanding the hot gases togenerate thrust to propel the engine, and an exhaust nozzle for allowinghot gases to exit the engine. Thus, the exhaust nozzle must accommodateextremely hot gases exiting the engine.

In military operations, design of planes to avoid detection by radar hasbecome an important issue. The ability of the plane to remainundetected, also referred to as a signature of a plane, depends on theoverall geometry of the plane and materials the plane is fabricatedfrom. To minimize detection, it is preferable to eliminate gaps betweenengine parts and to achieve certain smoothness for the outer shape ofthe engine. Additionally, it is preferable to avoid use of metals on theouter surfaces of the engine.

Other considerations critical to engine design are avoiding air leakageand insulating certain engine components from exposure to hot gases. Onetype of a material that withstands hot temperatures is ceramic matrixcomposite (or CMC), material. However, it is difficult to attach the CMCmaterial components to metal components. One obstacle to attaching theCMC material to the metal is different thermal expansions of thematerials. In general, it is difficult to attach or join differentmaterials in a gas turbine engine due to different thermal expansionproperties.

SUMMARY OF THE INVENTION

According to the present invention, a fastener assembly for attaching anon-metal component to a metal component includes a fastener having abase portion and a protruding portion with the base portion having ashape complementary for mating with an attachment feature formed withinthe non-metal component such that the base portion is retained withinthe non-metal component. The protruding portion including a base end anda distal end with the distal end including a threaded portion. Thefastener assembly also includes a tightening means for attaching ontothe threaded portion of the protruding portion of the fastener such thatonce the base portion of the fastener is mated with the attachmentfeature of the non-metal component, thereby securing the fastener to thenon-metal component, the protruding portion of the fastener extends fromthe metal component to allow the tightening means to be attached ontothe threaded portion to secure the metal component between the non-metalcomponent and the tightening means.

The fastener assembly allows attachment of components fabricated fromdissimilar materials without forming through holes in one of thecomponents. Additionally, the fastener assembly compensates fordifferences in thermal expansion rates between the non-metal componentand the metal component while providing a tight attachment therebetween.

According to one embodiment of the present invention, the fastenerassembly attaches a plow portion of a divergent flap of a gas turbineengine onto a backbone structure of the flap wherein the plow portion isfabricated from CMC material and the backbone structure is fabricatedfrom metal.

The foregoing and other advantages of the present invention become moreapparent in light of the following detailed description of the exemplaryembodiments thereof, as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic depiction of a gas turbine engine;

FIG. 2 is a schematic side elevational view of a divergent flap and anexternal flap of the gas turbine engine of FIG. 1;

FIG. 3 is a schematic side elevational view of the divergent flap ofFIG. 2 with a plow portion shown in cross-section;

FIG. 4 is a schematic top view of the divergent flap of FIG. 3;

FIG. 5 is an enlarged, partial view of the divergent flap of FIG. 3showing the plow portion in cross-section during non-operationalcondition;

FIG. 6 is an enlarged partial view of the divergent flap of FIG. 3showing the plow portion in cross-section during operational condition;

FIG. 7 is a schematic, perspective, broken-away view of a plow fastenerassembly attaching a hotsheet of the divergent flap to a bracket;

FIG. 8 is an exploded view of the plow fastener assembly of FIG. 7attaching the hotsheet and the bracket;

FIG. 9 is a schematic cross-sectional view of the plow fastener assemblyof FIG. 8 taken along line 9—9;

FIG. 10 is a schematic cross-sectional view of the plow fastenerassembly of FIG. 8 taken along line 10—10;

FIG. 11 is a cross-sectional view of an attachment fastener assemblysecuring a hotsheet and a backbone structure of the divergent flap ofFIGS. 3 and 4 with the attachment fastener assembly passing through asubstantially round hole; and

FIG. 12 is a cross-sectional view of an attachment fastener assemblysecuring the hotsheet and the backbone structure of the divergent flapof FIGS. 3 and 4, with the attachment fastener assembly passing throughan elongated slot.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Referring to FIG. 1, a gas turbine engine 10 includes a compressor 12, acombustor 14, and a turbine 16 centered around a central axis 17. Air 18flows axially through the engine 10. As is well known in the art, air 18is compressed in the compressor 12. Subsequently, the compressor air ismixed with fuel and burned in the combustor 14. The hot gases expandgenerating thrust to propel the engine 10 and to drive the turbine 16,which in turn drives the compressor 12. The exhaust gases from theturbine 16 exit through the exhaust nozzle 20.

Referring to FIG. 2, the exhaust nozzle 20 includes a plurality ofexternal flaps 24 arranged circumferentially about the axis 17 and aplurality of divergent flaps 26 disposed radially inward from theexternal flaps. Each external flap 24 includes an external flap surface28 having a particular geometry. Each divergent flap 26 includes a foreportion 30 and an aft portion 32. The fore portion 30 includes a hingeassembly 36 for securing the divergent flap 26 to the gas turbineengine. The divergent flap 26 further comprises a hotsheet 38 extendingthe length of the flap 26 from the fore portion 30 to the aft portion32, a backbone structure 40 disposed radially outward of the hotsheet 38and secured thereto by means for attachment 42, and a plow portion 46disposed in the aft portion 32 of the divergent flap 26 and secured tothe backbone structure 40 by a plow fastener assembly 48, shown in FIGS.3–10.

Referring to FIGS. 3 and 4, in the preferred embodiment of the presentinvention, the hotsheet 38 comprises a substantially flat substratefabricated from ceramic matrix composite (CMC) having a hotsheet innerside 50 exposed to the exhaust gases 18 and a hotsheet outer side 52facing the backbone structure 40. The hotsheet inner side 50 and thehotsheet outer side 52 extend from the fore portion 30 to the aftportion 32 and include a hinge edge 56 and a trailing edge 58. In thepreferred embodiment, the trailing edge is defined by a chamferedsurface 60. The hotsheet 38 also includes a plurality of attachmentopenings 61, as best seen in FIG. 4. The openings 61 also include acountersink hole 62 formed within the hotsheet inner side 50, as bestseen in FIG. 11.

The backbone structure 40 extends the length of the hotsheet 38 andprovides structure thereto. In the preferred embodiment, the backbonestructure 40 is fabricated from metal. Additionally, in one embodimentof the present invention, the backbone structure 40 includes an aftsupport 63 extending into the aft portion 32 of the divergent flap 26,as best seen in FIG. 3. The backbone structure 40 also includes aplurality of backbone openings 64.

Referring to FIGS. 5 and 6, the plow portion 46 includes a plow body 66having a plow outer surface 68 and a plow inner surface 70, as well as aplow outward edge 72 and a plow inward edge 74. The plow outer and innersurfaces 68, 70 have a contour to minimize plane signature and toprovide optimal aerodynamic characteristics. In non-operating conditionof the engine, the plow 46 is not in register with the trailing edge 58of the hotsheet 38, as seen in FIG. 5. Rather, the plow 46 is disposedaxially inward from the chamfered surface 60 and forms an offset 75between the plow outer surface 68 and the chamfered surface 60. A gap 76is also formed between the hotsheet outer surface 52 and the plow inwardedge 74. In the preferred embodiment, the plow portion 46 is fabricatedfrom CMC.

Referring to FIGS. 6–10, the plow 46 is attached to the backbonestructure by means of the plow fastener assembly 48. In the preferredembodiment, the plow 46 includes attachment features 77 for attachingthe plow portion onto the backbone structure comprising a dovetail slot80 formed therein and a recess 82 also formed within the plow portion,as best seen in FIGS. 8 and 9. The recess 82 includes a substantiallyflat recess surface 83 and a recess wall 84. The dovetail slot 80includes a bottom slot surface 85 and wedge slot surfaces 86.

Referring to FIGS. 7 and 8, the plow fastener assembly 48 includes aplow fastener 94, a nut 96, and a bracket 98. The plow fastener 94includes a base portion 104 and a protruding portion 106 extending fromthe base portion. The protruding portion 106 includes a distal end 108and a base end 110 with threads 114 formed on the distal end 108. Thebase portion 104 has a substantially trapezoidal shape adapted to fitinto the dovetail slot 80 of the plow 46. The fastener includes a radius116 formed at the base end 110 of the protruding portion 106 of thefastener 94, as best seen in FIGS. 9 and 10. The nut 96 is adapted to befastened onto the threads 114 of the protruding portion 106 of thefastener 94. The bracket 98 includes a first side 118 and a second side120 with ribs 124 formed thereon. The ribs 124 are formed to fit intothe recess 82 of the plow 46, as best seen in FIGS. 8–9, and in thepreferred embodiment, are formed on opposite sides of an opening 126formed within the bracket 98. The opening 126 is adapted to allow theprotruding portion 106 of the fastener 94 to fit therethrough. ABelleville washer 128 can optionally be placed between the bracket 98and the nut 96.

Referring to FIGS. 8–10, as the plow fastener 94 is inserted into thedove-tail slot 80, a gap 130 is formed between the base portion 104 ofthe fastener 94 and the dovetail slot 80, as best seen in FIGS. 9 and10. The gap 130 and the radius 116 allow for thermal expansion of thefastener 94 and minimize loading of the CMC material of the plow. As theplow fastener 94 fits into the attachment features 77 of the plow, theribs 124 fit into the recess 82. The recess 82 includes thesubstantially flat recess surface 83 to accommodate the ribs 124. Therecess 82 and the ribs 124 ensure retention of the plow fastener 94within the plow 46. The Belleville washer 128 maintains the preload ifcomponents grow thermally. Although one Belleville washer 128 is shown,a plurality of washers can also be used.

Referring to FIGS. 3, 4, 11 and 12, means for attachment 42 of the CMChotsheet 38 to the backbone structure 40 includes a fastener 134, awasher 136, a spacer 138, at least one Belleville washer 140, and a nut142. The fastener 134 includes a head portion 146 and a body portion 148with the body portion including a plurality of threads 150. The fastener134 passes through the attachment opening 61 and the countersink hole 62formed within the CMC hotsheet 38. The fastener head portion 146 fitsinto the countersink hole 61. The washer 136 is sandwiched between thehotsheet 38 and the backbone structure 40 and supports the spacer 138.The spacer 138 includes a cylindrical portion 154 and a ring portion 156extending outwardly from the cylindrical portion. The cylindricalportion 154 of the spacer is substantially adjacent to the fastener body148 and the ring portion 156 extends radially outward from the backbonestructure 40 defining a spacer gap 158 therebetween, as best seen inFIGS. 6–12. The length of the cylindrical portion 154 of the spacer 138is greater than the thickness of the backbone structure 40 disposedtherein to define the gap 158. At least one Belleville washer 140 isdisposed radially outward from the spacer 138 with the nut 142 tightenedto clamp all the components together against the hotsheet 38 to apredetermined preload condition for a relatively tight fit without anylooseness between the hotsheet 38 and other components.

Referring back to FIG. 4, the backbone structure 40 includes theplurality of backbone openings 64 to allow attachment of the backbonestructure 40 onto the hotsheet 38. The backbone openings 64 proximate tothe hinge assembly 36 are substantially round and sized to accommodatethe body portion 148 of the fasteners 134, as seen in FIG. 11. Theremaining backbone openings are formed as elongated slots to allow formovement of the backbone structure 40 relative to the hotsheet 38, asseen in FIG. 12. Thus, the backbone structure 40 is fixedly attached tothe hotsheet at the fore portion 30 of the flap 26. However, thebackbone structure 40 is free to translate axially as a result ofthermal expansion toward the aft portion 32 of the flap 26.

In operation, once the engine 10 begins to operate, the temperature ofthe engine quickly rises from the ground ambient temperature to extremehigh temperatures. The temperature of the gases 18 passing through theengine also rises resulting in extremely high temperatures and createsharsh environment for a majority of the gas turbine components. Morespecifically, as the engine 10 begins to operate, the hot gases 18 areexhausted through the exhaust nozzle 20 causing the divergent flap 26 toheat to very high temperatures. The hotsheet 38 is in contact with theexhaust gases 18 exiting the engine. The hotsheet 38 is specificallydesigned to withstand the hot temperatures. Although the CMC hotsheet issubjected to extremely high temperatures, the hotsheet does not expand agreat deal due to the material properties of CMC. However, the metalbackbone structure 40 is subject to greater thermal expansion.Therefore, as the backbone structure 40 expands, the plow 46, secured tothe backbone structure, moves aft toward the trailing edge of thehotsheet 38. As the plow 46 shifts relative to the trailing edge 58 ofthe hotsheet 38, the offset 75 is bridged and is substantiallyeliminated. As the backbone structure expands, the plow outer surface 68becomes substantially flush with the chamfered surface 60 and theexternal flap outer surface 28, as best seen in FIGS. 2 and 6. Theextremely hot temperatures also cause the aft portion 32 of the hotsheet38 to warp and deflect. The aft support 63 of the backbone structure 40minimizes the deflection of the trailing edge 58 of the hotsheet 38. Byminimizing deflection, contact between the plow inward edge 74 and thehotsheet 38 is also minimized.

In the plow fastener assembly 48, the dovetail slot 80 retains thefastener 94 therein. The recess 82 provides a locking feature to preventrotation and translation of the fastener 94 with respect to the CMCsheet. The gap between the base portion of the fastener 94 and thedovetail slot 80 allows for thermal growth of the metal fastener withoutloading the CMC material. The Belleville washer can be placed betweenthe nut and the feature to maintain preload when the parts thermallyexpand and to reduce the stiffness of the fastener assembly to minimizeCMC stresses than can occur because of thermally induced tightening ofthe assembly.

The plow fastener assembly 48 allows attachment of a CMC sheet onto ametal structure without forming a through hole opening in the CMC sheet.Such feature is particularly critical in stealth plane design where theouter surface of the plane must be fabricated from particular materialsand must not include metal fasteners on the surface thereof.Additionally, this unique attachment provides a connection between theCMC material and metal structure without leakage since a need for holesor openings is eliminated. Furthermore, the fastener 94 is insulatedfrom the hot side 50 of the CMC sheet 38, thereby maintaining integrityof the fastener. The plow fastener assembly 48 can be used to join anyCMC material with metal structure. In one embodiment of the presentinvention, the plow 46 is attached to the backbone structure via thebracket 98, as shown in FIGS. 5–8. The bracket 98 is fabricated frommetal and can be easily attached to the backbone structure 40subsequently by various conventional fastening means 160, such as rivetsor bolts, as shown in FIGS. 5 and 6. Thus, the bracket 98 provides abridge between the CMC sheet and other components to which the bracketcan be attached by use of conventional fastening techniques. However, inthis particular case, the plow can be directly attached to the backbonestructure 40.

Although in a preferred embodiment the bracket 98 is included betweenthe plow portion and the backbone structure, the plow 46 could bedirectly attached to the backbone structure 46. However, the bracket 98provides a bridge between the plow portion and the backbone structure,thereby enabling the plow via the bracket to be attached to anystructure by various means of a conventional attachment. Additionally,in the preferred embodiment, the plow fastener assembly 48 is disposedin one plane to accommodate for thermal expansion and minimize thermalstresses. The fastening means 160 attaching the bracket 98 to thebackbone structure 40 are also disposed in such a plane to minimize anythermal stress. The backbone openings 64 formed as elongated slots anddisposed within the backbone structure also allow the backbone structure40 to thermally expand relative to the hotsheet 38, thereby moving theplow 46 toward the trailing edge 56 of the hotsheet.

The means for attachment 42 allows attachment of the CMC material toother types of materials without damaging the CMC material whileapplying significant tightening force to the assembly. As the nut 142tightened onto the fastener 134, the metal of the backbone structure 46is trapped between the spacer 138 and the washer 134 and all componentsare clamped together against the hotsheet 38 to a set preload for atight fit without looseness between the CMC material and othercomponents. The elongated slots 64 formed within the backbone structure40 allow movement of the backbone structure relative to the hotsheetwithout introducing looseness to the attachment assembly 42. TheBelleville washer 140 maintains preload and reduces the stiffness of thefastener assembly to minimize CMC stresses than can occur because ofthermally induced tightening of the assembly. The spacer allows for thethermal growth of the backbone structure while maintaining a tightattachment of the assembly.

One advantage of the present invention is that the plow 46 bridges thegap between the hotsheet 38 and the external flap 24. This featureensures a smooth overall contour of the engine to minimize detection ofthe plane. An additional advantage of the present invention is that theplow moves relative to the hotsheet 38 to bridge the offset 75 duringthe hot condition to further minimize detection of the plane. Anotheradvantage of the present invention is that the plow portion 46 isfabricated from the CMC material. The plow portion, fabricated from theCMC material, minimizes signature of the plane. The features of thepresent invention also accommodate different rates of thermal expansionof CMC and metal components. For example, the backbone openings 64 allowrelative movement between the backbone structure 40 and the hotsheet 38,thereby accommodating different rates of thermal expansion of metal andCMC material and also allowing the plow 46 to be moved toward thetrailing edge 56 of the hotsheet 38 to minimize even small gaps forfurther improving signature of a plane. Another advantage of the presentinvention is that the aft portion 63 minimizes deflection of thehotsheet 38. A further advantage of the present invention is that thebracket 98 allows attachment of the CMC sheet onto any material.

Additionally, the present invention overcomes the difficulty offastening a CMC plow portion onto metal components. The plow fastenerassembly 48 eliminates a need for forming through openings in theexternal surface of the engine and also compensates for different ratesof thermal expansion between metal and CMC.

One advantage of the means for attachment 42 is that the CMC panel canbe tightened with significant force and still allow sliding motionbetween the CMC panel and the metal structure. Additionally, anyrattling of the components within the opening is eliminated, therefore,minimizing degradation of the material and extending service life of thecomponents. This fastening scheme not only attaches the CMC component toa dissimilar material component, but also accommodates any thermalgrowth mismatch and secures the CMC component under positive andnegative pressure conditions. The fastening scheme permits sliding ofthe structure relative to the CMC panel to eliminate thermally inducedstresses.

While the present invention has been illustrated and described withrespect to a particular embodiment thereof, it should be appreciated bythose of ordinary skill in the art that various modifications to thisinvention may be made without departing from the spirit and scope of thepresent invention.

1. A fastener assembly comprising: a metal component having anattachment feature unitarily formed therewith; a non-metal componenthaving an attachment feature and an additional attachment feature formedwithin said non-metal component; a fastener having a base portion and aprotruding portion, the base portion having a shape complementary tosaid attachment feature formed within the non-metal component for matingtherewith such that the base portion is retained within the non-metalcomponent, the protruding portion including a base end and a distal end,the distal end including a threaded portion; and tightening means forattaching onto the threaded portion of the protruding portion of thefastener such that once the base portion of the fastener is mated withthe attachment feature of the non-metal component, thereby securing thefastener to the non-metal component, the protruding portion of thefastener extends from the metal component to allow the tightening meansto be attached onto the threaded portion to secure the metal componentbetween the non-metal component and the tightening means; saidattachment feature of said metal component mating with said additionalattachment feature of said non-metal component to minimize rotation andtranslation between said metal and non-metal components.
 2. The assemblyaccording to claim 1 further comprising: at least one washer disposedbetween the metal component and the tightening means.
 3. The assemblyaccording to claim 2 where the at least one washer is a Bellevillewasher.
 4. The assembly according to claim 1 wherein the additionalattachment feature is a recess formed within the non-metal component. 5.The assembly according to claim 4 wherein the recess has a substantiallyflat surface to allow proper mating between the non-metal and metalcomponents.
 6. The assembly according to claim 1 wherein the metalcomponent attachment feature is a rib adapted to mate with theadditional feature formed within the non-metal component.
 7. Theassembly according to claim 6 wherein a gap between the base portion andthe dovetail slot is formed in non-heated condition of the components toallow for thermal expansion of the base portion into the dovetail slot.8. The assembly according to claim 1 wherein the non-metal componentattachment feature is a dovetail slot and the base portion hassubstantially trapezoidal shape to mate with the dovetail slot of thenon-metal component.
 9. The assembly according to claim 1 wherein thetightening means is a nut.
 10. The assembly according to claim 1 whereinthe non-metal component is fabricated from ceramic matrix compositematerial.
 11. The assembly according to claim 1 wherein a radius isformed at the base portion of the protruding portion of the fastener torelieve stresses induced by thermal expansion.
 12. A fastener assemblycomprising: a plow portion having an attachment feature and anadditional attachment feature formed within said plow portion; abackbone structure having an attachment feature unitarily formedtherewith; a fastener having a base portion and a protruding portion,the base portion having a shape complementary to, and for mating withsaid attachment feature formed within the plow portion such that thebase portion is retained within the plow portion, the protruding portionincluding a base end and a distal end, the distal end including athreaded portion; and tightening means for attaching onto the threadedportion of the protruding portion of the fastener such that once thebase portion of the fastener is mated with the attachment feature of theplow portion, thereby securing the fastener to the plow portion withoutforming through holes within the plow portion, the protruding portion ofthe fastener extends from the backbone structure to allow the tighteningmeans to be attached onto the threaded portion to secure the backbonestructure between the plow portion and the tightening means; saidattachment feature of said backbone structure mating with saidadditional attachment feature of said plow portion to minimize rotationand translation between said backbone structure and plow portion.